Not Applicable
Not Applicable
1. Field of the Invention
This invention is in the field of apparatus used to remove debris from a well bore. Specifically, this invention applies magnetic force to attract magnetic debris to the tool, after which the tool can be withdrawn from the well bore to remove the debris.
2. Background Art
In the process of drilling an oil or gas well, producing oil or gas from the well, or refurbishing an existing well, tool failures and normal operation often result in the depositing in the well bore of various kinds of debris. Downhole milling of metal items produces metallic mill cuttings which often are not completely removed from the well bore by circulation of milling fluid. Furthermore, bit cones, bearings, slips, tong pins, and hammers, or fragments thereof, can collect at the bottom of the well bore. Several devices have been developed for the removal of such debris from the well bore.
Tools incorporating a basket often circulate fluid up the annulus at a rapid rate, to carry the debris upwardly to an area of reduced flow rate where the debris falls back, to settle into a basket for retrieval. Other basket tools use a venturi effect to draw debris into the tool, usually at the bottom end, then it is caught in a basket within the tool. Debris which is magnetic, or susceptible to magnetic attraction, can be attracted to a tool which incorporates magnets, followed by removal of the tool and its attached debris from the well bore. Some such tools have a magnet in the lower end of the tool, for the purpose of attaching magnetic debris to the lower end of the tool.
Another tool has been devised which has a plurality of magnets aligned in a string in a cavity near the outer surface of the tool, covered by a thin metal housing. Yet another tool has been devised which has a plurality of magnets individually embedded into a plurality of recesses in the outer surface of the tool, around its periphery. In this type of tool, nonmagnetic cups may be pressed or brazed into the recesses, and a set pattern of magnets are essentially permanently retained in the nonmagnetic cups by means of epoxy, or some other adhesive. The magnets are typically exposed to the well bore environment surrounding this tool, subjecting them to physical damage or corrosion in the well bore. Further, the exposed magnets are subject to physical damage during the process of cleaning debris from the tool after it is withdrawn from the well bore. Still further, the exposed magnets may even be lost in the well bore when the retaining epoxy becomes soft because of high well bore temperature.
It would be desirable to have a magnetic debris retrieval tool in which magnets could be placed in a choice of patterns on the outer perimeter of the tool and easily removed therefrom. It would also be desirable to cover the magnets with protective covers, and to magnetically isolate the magnets from the remainder of the tool to enhance their performance.
By way of example, the preferred embodiment of the present invention is a tool for removal of magnetically susceptible debris from a well bore, by causing the debris to adhere to the body of the tool and removing the tool from the well bore. The tool body has a plurality of recesses in its outer surface. A plurality of magnets can be inserted in selected recesses to form a desired pattern of magnets. The magnets are retained in the recesses by retainer caps which thread into the recesses. The retainer caps are designed to fit entirely within the recesses, to give the tool a streamlined aspect, or an unobstructed outer surface. The retainer caps may be small enough to fit entirely within the recesses, threaded therein by the use of some low profile drive contour, such as a hexagonal head, a recessed hexagonal shape, or a screwdriver slot. Alternatively, the retainer cap may be threaded into the recess by the use of a drive member which can subsequently be removed from the retainer cap, by the application of higher torque to shear the drive member away, or by some similar operation. The retainer caps can be constructed of a non-magnetic material, and non-magnetic spacers can be placed beneath the magnets, to isolate the magnets from the tool body, thereby enhancing the performance of the magnets.
The novel features of this invention, as well as the invention itself, will be best understood from the attached drawings, taken along with the following description, in which similar reference characters refer to similar parts, and in which: